This invention is particularly suited to joining honeycomb panels, each panel having a cellular core of hexagonal honeycomb sandwiched between lightweight cover sheets. This invention solves the problem of permanently fastening two adjacent panels by using a hollow, threaded pin driven by a unique drive assembly which, when attached to a drill, injects epoxy resin through the pin and into the area surrounding the joint.
The present method of joining composite panels having a structural or Nomex.RTM. honeycomb core is a time consuming and labor intensive means of constructing certain vehicular interior products. These products range from interior bulkheads to cabin furniture such as galleys, tables, closets, and the like. These products are constructed of the lightweight composite panels much in the same fashion as wood cabinetry except for the joining methods which present a problem, since there is no solid core in the panels.
The panels range in thickness generally from 1/2" to 1-1/4" and have fiberglass "pre-preg" (heat activated resin) coated skins or aluminum skins of varying thickness to form a "sandwich." The panels are formed flat or curved over a tool and placed in a large oven under heat and vacuum pressure for a specified period of time. Cabinetry constructed of this material offers high structural strength and good rigidity with the benefit of ultra light weight compared to plywood and other conventional products.
However, the absence of a dense core results in insufficient structural or rigid mass for retaining purchase on a screw or any conventional type of fastener. The present methods of joining such lightweight, honeycomb core composites include epoxy bonding, angle corner brackets with special sandwich panel fasteners, edge bonding with hollow pins set in epoxy and surface bonding overlapping joints. Such methods of joint construction are expensive and time consuming for the following reasons:
1. Panels must be edge-filled with a bonded wood strip or an epoxy filler before final covering.
2. Through-fasteners must be installed through edge filling, or spot filling, or inserting wood in the area to prevent crushing of the core material.
3. Pins or hollow dowels set in epoxy commonly used in tee or angle joining must be installed in four steps. The steps include drilling through the adjoining panels forming the joint. The core is then removed beyond the diameter of the drilled hole in the panel's skin. Panels are positioned with their bores aligned, and the pin inserted. Next, epoxy is mixed and installed to set the pin. The epoxy is allowed to cure for a specified period of time, hardening and joining the panels.
4. Angle extrusion methods of joining panels require the placement of angles (in a fixture) at the corners of adjoining panels. Holes must be drilled first in the flanges of the extrusion and then through the panels with core removed beyond the skin as noted above. Special "through type" fasteners, i.e., Delron.RTM., are then installed and set in epoxy. These are threaded for receiving conventional machine screws inserted through the angles to cinch the connections.
Applicant's "Drill-Loc.TM." system is unique in its method of installation and fastening for several reasons. First, it has its own unique fastener pin with a pilot drill point, having a stepped end which locates and drills the pilot hole and the larger hole while removing core material. Second, the pin is hollow throughout its body and contains drill point jets to dispense epoxy into the hole and around the pin and "set" the pin in the panels. Third, the helical threads of the pin lock the pin to the core material in the panel and help remove core chips from the hole during the drilling phase. Finally, the pin employs a special flange head having dowel holes to couple with a special drill-mounted drive assembly and epoxy container. A slight flare is incorporated in the head of the threaded body to seat the pin into the skin, producing a tight fit and achieving a flush fit with the panel's surface. The head of the pin, having locked itself to the surface skin of the panel via its thread, insures a tight integral connection of the mating panels once the epoxy is cured. These and other unique features of the invention are more fully set forth herein.
Other patents have disclosed methods for joining lightweight panels, such as honeycomb core panels. U.S. Pat. No. 4,370,372 (Higgins et al. 1983) discloses a fastener comprised of a rigid aluminum tube about 2" long and having a diameter of about 5/16", open at both ends, flared at one end and having a series of longitudinal and peripherally spaced apertures along the wall of the tube.
The first step of the method disclosed in the '372 patent is to form coacting bores in the respective honeycomb panels to receive the fastener elements, such as by drilling holes with a conventional electric drill. The drilling step causes a rupture of the honeycomb bores which the drill bit engages. The bores are cleaned out and aligned, the hollow fastener inserted, and a liquid anchoring fluid is pumped or applied through the flared end of the fastener. The liquid forms a continuous column inside the fastener and spreads out of the tube and longitudinally into the ruptured honeycomb regions. The liquid adhesive hardens, forming a unitary column with the hollow tube fastener, thus permanently anchoring the two panels.
In summary, the '372 patent requires: drilling a hole through the work pieces, fly-cutting the core within the panel skins and removing the chips, uncapping and mixing the epoxy, filling the hole with the epoxy mix using first a disposable caulk nozzle and then a spatula, pressing the pin in by hand, wiping off the excess epoxy mix from the panel surface.
It is to be noted that the '372 pin does not mechanically attach itself at the panel skin line, and thus loses strength as the components rely on a thin film of resin lying between the flange and the skin of the panel. The methods and apparatus disclosed in the '372 patent, however, are time-consuming as they require the several discrete steps of drilling, inserting, and injecting the fluid.
The present invention, on the other hand, reduces the steps and time required to join lightweight panels by using a unique threaded pin and a unique drive assembly which, in one step, joins the two panels with the threaded pin and mixes and injects an adhesive fluid, such as epoxy, through the pin into the ruptured cells adjacent to the pin bore.
Thus, it is the object of the present invention to provide a unique method and apparatus for joining lightweight panels.
It is a further object of the present invention to provide a system having a unique pin comprised of a threaded tube, open at one end, with a means for attaching the open end to a unique drive assembly. The system (drive assembly and pin) attached to a drill, will rotatably insert the self-tapping pin through the panels to be joined, and upon seating of the pin head flush with the panel surface, will mix and inject an adhesive fluid, such as epoxy, through the hollow pin out dispersion jets into the panel. The liquid so injected will harden and form a continuous column within the ruptured cells, and around the threaded portion of the pin, thus joining the panels.
It is a further object of the present invention to provide for a unique drive assembly comprising a housing dimensioned to accept a widely available, "off the shelf" epoxy cartridge, the cartridge having two piston-driven reservoirs, one reservoir for the epoxy and one for the hardener. The drive assembly is provided with a means for retaining a unique hollow, self-tapping pin to drill the pin into adjacent lightweight panels and is further provided with a means to drive mixed epoxy/hardener through the pin into the panels for a fixed, permanent joint.
It is a further object of the present invention to provide the unique cartridge housing with a plunger means for clutchably engaging the housing means. The plunger means engages the pistons of the epoxy cartridge. With the clutch of the housing assembly engaged and the pin seated on a nose portion thereof, the drill rotates the assembly until the pin is seated into the panel. Upon seating, the increased torque then disengages the clutch and allows the plunger to force the epoxy and the hardener through a mixing nozzle into the hollow pin. The mixed composition is thus injected through dispensing jets in the nose and/or body of the pin into the shattered honeycomb cells and around the threads of the pin.
Other objects of the invention will become readily apparent to those skilled in the art upon reviewing the specification and claims set forth herein.